There are more than 700 types of pure bred dogs in the world. They were first domesticated by cavemen in the Paleolithic Age. Here are some interesting facts about dogs.

1. Dogs can register sounds of 35,000 vibrations a second where as a human can only hear 20,000 vibrations. 2. A German shepherd has smell sensory cells of 220,000,000 where as a human has only 5,000,000 cells 3. Theobromine in chocolates, a substance similar to caffeine, can kill the dogs, or at the very least make them seriously ill. 4. The tallest dogs are the Great Dane and the Irish wolfhound. The smallest dogs are the Chihuahua, Yorkshire terrier and Toy Poodle. 5. The oldest age recorded for a dog is 29 years and 5 months. 6. The world's heaviest and longest dog is an English Mastiff named Zorba which weighed 3423 pounds and eight feet three inches long from nose to tail. 7. Laika was the world's first ever space astronaut dog which was sent into space in 1957 by the Russian government. 8. Greyhounds can reach speeds of up to 45 miles per hour in short bursts. 9. In Second World War, Russians trained dogs to run suicide missions between the tracks of German tanks with mines strapped on their backs. 10. In the Middle Ages, Mastiffs used to be dressed in light armor to which was strapped a pot of flaming sulphur and were then made to run into battle against mounted knights.